This Application claims priority of PCT application WO 00/49418 which is based on German Patent Application 199 06 409.1 filed Feb. 16, 1999.
The present invention relates to a dosing device and to a method for operating a dosing device.
A dosing device which is used in practice, comprises at least one withdrawal container and a dosing means which is in line communication with the withdrawal container and discharges the medium to be dosed to receiving containers. Such a dosing system may e.g. be of a multi-channel type including a piston system; its technical construction is complicated and it consists of high-quality materials and is thus an expensive construction. Further problems arise from wear which is normally high. Furthermore, a change in the medium requires a troublesome cleaning process, and tests carried out with a current device have revealed that it is difficult, particularly when using media, to adequately clean and, if necessary, sterilize the pistons systems because the piston systems often comprise undercuts of complicated shapes.
It is therefore the object of the present invention to provide a dosing system of the construction of which is much more simple than those of known dosing systems and which is thus less complicated from a structural point of view and can be operated more easily.
In the inventive dosing device, the dosing means comprises at least one dosing unit which is constructed as a uniform piston-cylinder unit designed as a disposable member. This has the effect that, in contrast to known dosing devices, the piston-cylinder unit can easily and efficently be replaced, and disposed of, if necessary. The present invention permits the elimination of the cleaning effort for the dosing means. This is of particular advantage in dosing devices in which the media has to be changed often or which are operated with media that soils the dosing means, and impairs the operability thereof. In known systems great efforts are taken for a frequent cleaning whereas the dosing device of the invention just requires a replacement of the disposable member or members.
Preferably, the piston-cylinder unit is designed as a plastic member whose material is not valuable and which can be recycled in an environment-friendly manner.
For the operation of the dosing means, a particularly preferred embodiment provides for a motor type drive means which drives a coupling means in a longitudinally displaceable manner via a suitable motion converter or gearing. The coupling means, in turn, can be secured to the piston of the piston-cylinder unit so that for the installation of the disposable member the latter need just be inserted into the dosing means and has to be connected with its piston to the drive means via the coupling means.
The dosing unit, in turn, is connected to a valve means which is arranged in the flow path between the withdrawal container and the receiving containers. In a particularly preferred embodiment the valve means comprises a suction valve and a discharge valve which are each preferably designed as check valves arranged in a valve housing or valve head for forming a separable operable and compact uniform component. When the piston of the piston-cylinder unit is moved upwards during operation of the dosing device, a negative pressure is created in the valve head whereupon the suction valve is opened and the medium to be dosed can be sucked in accordingly. In the case of an overpressure, i.e. when the piston of the piston-cylinder unit is pressed downwards, the ejection valve is opened and the dosing operation can be carried out.
Apart from the cylinder-piston units, the valve means, in particular the valve head and the other members of the valve means, may be designed as disposable members, which are in particular made from plastics. The invention is simple in operation because the piston-cylinder units and the valve means can be assembled and disassembled by simple operations rapidly, reliably, in a leak-proof manner and detachably without the need for any tools.
To further improve such an easy operability, the cylinder of the piston-cylinder unit is provided in a particularly preferred embodiment with a threaded connection (in particular a Luer lock connection) and with a sealing cone cooperating with a counter-cone in the valve head. With a corresponding design of the threaded connection, the cylinder can thereby be fixed through half a rotation to the valve head and also tightly connected to the valve head via the two cooperating sealing cones.
The valve head itself can also be tightly mounted on a simple connection pin by being simply attached thereonto. Thus, a special advantage in the inventive dosing device is in particular obtained when the piston-cylinder units and the valve means have to be used as sterilized members. According to the principles in the invention these may be sterilized during production and thus delivered as pre-sterilized members and installed and, after use, they can be easily and efficiently disassembled and disposed of to be replaced by new pre-sterilized members. This offers special advantages insofar as a complicated cleaning process can be dispensed with which would require a previous disassembly of said members and a subsequent sterilization and reinstallation of said old members.
In a further, particularly preferred embodiment, the valve means is arranged on a distributor rail which is in flow communication via a connection line with the withdrawal container. The connection line is preferably designed as a channel which is integrated into the distributor rail and which in a further, particularly preferred embodiment is in flow communication with a bottom member of a compensating container via a connecting bore. The valve means is brought into flow communication with the distributor rail via suitable connection members, such as connection nipples.
The compensating container which is arranged between the withdrawal container and the dosing unit serves to maintain a substantially constant suction pressure; to this end, in a further, particularly preferred embodiment sensors are provided on the compensating container for determining the filling volume. Said sensors can control a pump positioned within the delivery path for the basic delivery of the medium into the compensating container, so that said container has a substantially constant filling volume, which, in turn, ensures a substantially constant input pressure in the valve means.
The provision of the compensating container is advantageous when dosing units of plastics are provided, as their elasticity and inherent conveying inaccuracy can thereby be compensated. In such dosing units only a relatively small suction pressure is allowed to prevail because otherwise the piston-cylinder units would leak and thus become inaccurate as to their delivery rate.
Moreover, a further particularly preferred feature of the compensating container is that it can be provided with a sterile filter if an operation under sterile conditions is required.
Finally, it is possible to support the dosing means such that it is displaceable within the dosing device; to this end the whole dosing means may e.g. be supported to be displaceable along a rail.
A method for operating a dosing device is also provided. In one aspect of the inventive method, a defined drop retraction into the ejection cannula of the dosing means or unit is achieved.
For this purpose, and after dosage, the piston of the piston-cylinder unit is retracted a short defined distance, which relieves the liquid column inside the dosing unit and thus retracts the drop. This is accomplished with the valve body because of its elastic material which will deform upon retraction of the piston of the piston-cylinder unit, thereby permitting a retraction of the liquid column. The one advantage of the invention is that a displaceable dosing unit does not splash any drops which would soil the whole device or system.
Of course the dosing device according to the invention can be adapted to different applications and in many ways. In particular, it is possible to provide a plurality of withdrawal containers and above all a plurality of dosing units of which all are arranged in the dosing means and provided with piston-cylinder units designed as disposable members. Such adaptations are all within the scope of the principles of the present invention.
Further details, features and advantages of the present invention will become apparent from the following description of an embodiment taken in conjunction with the drawings: